Apple has created a situation where it's impossible to replace a failed part with an identical one -- each part has a programmed unique ID (and perhaps related encryption).
What consumers have done is repair the phone with an *equivalent* part -- quite similar to what an Apple Store would have done.
Apple has the technical capability to allow the firmware to accept or reject the repair part. They can even do that with a process that retains the designed-in security. But they choose not to in order to lock in consumers.
Biting the hand that feeds IT
